Several different types of adhesive materials have been used in recent years in the fields of semiconductors and liquid crystal displays, for anchoring of electronic parts and for circuit connection. As such uses continue to require higher density and higher definition, the adhesives used must also exhibit higher adhesive force and reliability. The adherends used in bonding include printed circuit boards, organic substrates composed of heat resistant polymers such as polyimides, and metals such as copper, tin, nickel or aluminum and other inorganic materials such as ITO, Si3N4 and SiO2. Adhesives are also used for bonding between different types of the substrates mentioned above. The adhesives must therefore exhibit a wide range of properties in addition to superior adhesion, including high heat resistance and high reliability under high-temperature, high-humidity conditions, while also having a molecular design suitable for each adherend.
In particular, anisotropic conductive adhesives having conductive particles dispersed in adhesives are employed as circuit-connecting materials (circuit-connecting adhesives) used for connection between circuits such as between liquid crystal displays and TCPs, between FPCs and TCPs or between FPCs and printed circuit boards. Such adhesives used for semiconductors and liquid crystal displays have conventionally been thermosetting resin compositions comprising epoxy resins that exhibit high adhesion and high reliability (for example, see Patent document 1).
The constituent components of thermosetting resin compositions include epoxy resins and curing agents such as phenol resins that are reactive with epoxy resins. Thermal latent catalysts that promote reaction between epoxy resins and curing agents are also sometimes included in adhesives. For example, one-pack type epoxy resin adhesives employing thermal latent catalysts are employed in film, paste or powder forms since they do not require mixture of the base compound (epoxy resin) and the curing agent and are convenient to use. The thermal latent catalysts are major factors determining curing temperature and curing speed, and various compounds are used as thermal latent catalysts from the viewpoint of room temperature storage stability and curing speed during heating.
In actual adhesion steps using such adhesives, the adhesives are cured under curing conditions with a 170° C.-250° C. temperature for 1-3 hours to obtain the desired adhesive force. However, as the increasing integration of semiconductor elements and higher precision of liquid crystal devices in recent years are leading to ever narrowing pitches between elements and wirings, the heating of curing can produce adverse effects on the surrounding materials. In addition, the electrode widths and electrode spacings are becoming even more extremely narrow while electrode heights are decreasing. Therefore, it is not always possible to achieve sufficient adhesive force with conventional circuit connection adhesives, and problems such as shifting of wirings can occur. Moreover, since another goal is to shorten the duration of adhesion steps to reduce cost, it is desirable to accomplish curing and bonding at lower temperatures and in shorter times.
Radical-type adhesives which combine radical polymerizing compounds such as acrylate derivatives or methacrylate derivatives (hereinafter referred to as “(meth)acrylate derivatives”) with peroxides as radical polymerization initiators have become objects of interest in recent years as means of achieving lower temperature and shorter times. Radical curing with adhesives can be accomplished at low temperature and in a short period of time because of the high reactivity of the reactive radical species (for example, see Patent document 2). However, it has been noted that the adhesive strength is inferior to that of epoxy resins because of the high cure shrinkage during curing of the radical curing adhesives. It has been found that the adhesive strength for inorganic material or metal material substrates is particularly low.
Methods of enhancing adhesive strength, such as methods of imparting pliability by including ether bonds in cured adhesives in order to increase the adhesive strength, have therefore been proposed (see Patent documents 3 and 4). Such enhancing methods employ urethane acrylate compounds as the radical polymerizing compounds.    [Patent document 1] Japanese Patent Application Laid-open No. 1-113480    [Patent document 2] Japanese Patent Application Laid-open No. 2002-203427    [Patent document 3] Japanese Patent Publication No. 3522634    [Patent document 4] Japanese Patent Application Laid-open No. 2002-285128